Today, there are various media sources, such as digital broadcasting, VOD (Video On Demand) broadcasting, DVD (Digital Versatile Disk), and Blu-Ray® disk, and users enjoy these sources while switching from one source to another freely. However, a producer or broadcasting station differs for each source, so that audio recording level or audio dynamic range often differs between the media sources, resulting in output of surprising loud sound or output of poor sound that is hard to hear at the time of switching from one program to another or from one source to another. Accordingly, inconveniently, the user needs to adjust the volume to a desired level every time the volume is changed.
There are proposed some techniques for adjusting the above difference in volume or dynamic range between media sources. For example, there is known a technique that performs gain adjustment for respective signals obtained by frequency division and adds the resultant signals once again for averaging a signal level (refer to Patent Document 1). Using this technique prevents the lack of a high-frequency component to thereby prevent sound from being made unclear.